This invention relates to a window structure including a support for a flexible sheet of polymeric film to maintain the film in a planar configuration between a pair of opposed and spaced frame channels separating two panes of glass.
There have been triple pane windows to reduce heat loss but the present invention proposes the placement of a rectangular film between the panes of glass. The film will form an additional dead air space and further may be coated to vary the transmission characteristics for radiation of certain wavelengths. It is desirable that the support for the film occupy as narrow an area as the conventional frame spacing between the panes of glass in the dual pane window. It is essential to the aesthetics and to the use of the window that the film be optically planar. The present invention thus provides a window structure with the film supported in an optically planar configuration and provides a light weight, energy efficient structure which can be tailored to the desired energy transmission characteristics.
Prior to this invention there were structures for supporting flexible material such as metal or plastic screens, trampoline canvases, draperies, sign panels, etc. These structures typically fasten the material by connecting the material to the frame at intervals along its edges. These structures also exemplify uses of a supported sheet in which there is no concern for maintaining the supported sheet in an optically planar configuration. In some situations the natural configuration of the supported sheet as it hangs is adequate. Other situations utilize the natural tendency for the filaments within the fibrous material to slip with respect to each other and thus compensate for the applied stresses at the fastening points. This type of compensation cannot occur, however, with amorphous structures such as oriented polymeric films with which the stress areas are retained in the sheet and not compensated for by the change in the sheet structure. Thus, when the amorphous material is stretched across a surface and held within a slot by a rigid clip, or when the edge is secured at intervals with eyelets or other fasteners, little compensation for dimensional changes occurs and wrinkles will appear in the structure where pressure points exists. These wrinkles are very undesirable in a window and cause distortion. The need for a fastening structure to maintain a film between the glass panes in an optically planar or flat configuration for extended periods and numerous temperature cyclings was apparent. The solution however was difficult especially when the supported films were to be used within a large window or door assembly.